Starch (Chd 6H.sub.10 O.sub.5).sub.x is available from a variety of natural sources including most cereal grains, tubers, roots, and other plant parts. Starch can be used in a wide variety of applications ranging from adhesives to major food ingredients or critical food functional additives. The current invention is primarily directed to an efficient method of obtaining essentially pure starch, along with a protein concentrate, with excellent qualities for food preparation.
The starch content of legumes ranges from 35 to 60% of the dry weight of the beans. Legume starches have been identified as a new and exciting food ingredient. For example, pea starch has been used widely in the processed meat industry where heat and mechanical stability are of great interest. In canned foods, cooked sausages, pates, and other foods, pea starch can substitute for traditional starches with excellent results. As a thickening agent in soups and sauces and in many other products, pea starch gives a pleasant mouth feel. Heat stability, excellent expansion properties and marked resistance to mechanical shear are important in extruded products. Until now, the main limitation of the use of pea starch in foods is the relatively high cost of its isolation.
Most legume starch isolation methods are lengthy, laborious, and costly. Techniques for the isolation of legume starches were originally reported by Kawamura et al. (Kawamura, S., Y. Tuboi, T. Huzii [1955] "Studies on legume starches. I. Microscopic observation on the granules of starches from some Japanese legumes," Tech. Bull. Kagawa Agr. Coll. 7:87-90) and Kawamura et al. (Kawamura, S., M. Tada [1958] "Legume starches. III. Separation and determination of amylose and amylopectin. I. Introduction and preliminary experiments with iodine coloration," Chem. Abstr. 52:20428h). The Kawamura method involves treatment of a legume preparation with a 0.2% NaOH solution, washing with water, and dehydration with ethanol and water. See also Deshpande, S. S., S. Damodaran (1990) "Food legumes: Chemistry and technology," Chapter 3 In, Vol. X, Adv. Cereal Science & Technol. (Y. Pomeranz, editor) Am. Assoc. Cereal Chem., St. Paul Minn., pp. 147-241). The procedures most widely used today are three methods developed by Schoch et al. (Schoch, T. J., E. C. Maywald [1968] "Preparation and properties of various legume starches," Cereal Chem. 45:564-573), who identified certain conditions for starch isolation from legumes. In the first method, which is used for mung beans, garbanzo beans, and dehulled split yellow peas, starch can be obtained by initially steeping legume seeds in warm water in the presence of toluene to prevent fermentation. This initial steeping is followed by wet grinding and repeated screening. A second methods exists for lentils, lima beans, and white navy beans. The initial steps of the second method are similar to the first method but the second method further involves resuspension in a 0.2% NaOH solution (to dissolve most of the protein) and several tabling steps. The third method (for wrinkled seeded peas) requires exhaustive alkaline steeping and washings of the isolated starch.
The separation of pure legume starch is difficult because of the presence of a highly hydrated fine fiber (cotyledon cell wall material) and strong adherence of large amounts of insoluble proteins. The above procedures, or modifications thereof, were used recently, among others, by Haase et al. (Haase, N. U., W. Kempf, G. Tegge, U. D'heur [1987] "Vergleichende Untersuchungen zur Erbenstarkeisolierung auf nasstechnischen Wege," Die Starke 39:416-421), Honingfort (Honingfort, T. [1988] "Versuche zur Gewinnung and Charakterisierung yon Starke aus Erbsen, M. Sc. Thesis. U. Berlin, Inst. Food Technol., Dept. Cereal Technology.), and Hoover et al. (Hoover, R., S. C. Rorke, A. M. Martin [1991] "Isolation and characterization of lima bean Phaseolus lunatus starch," J. Food Blochem. 15:117-136). Vose (Vose, J. R. [1977] "Functional characterization of an intermediate amylose starch from smooth-seeded field peas compared with corn and wheat starches," Cereal Chem. 54:1141- 1151) prepared pea starch by pin milling whole peas, air classification of the very fine flour, defibering the starch concentrate, washing and repeated centrifugation. Unfortunately, this procedure is very damaging to the starch. Therefore, to obtain a product with minimum starch damage, the Schoch et al. ([1968], supra) method is required. Olsen (Olsen, H. S. [1978] "Continuous pilot plant production of bean protein by extraction, centrifugation, ultrafiltration, and spray drying," Lebensm.-Wiss. Technol. 11(2):57-64) described a batch and continuous ultrafiltration method for isolation of fababean protein isolates. The process can be used to obtain pea starch as a by-product. Colonna et al. (Colonna, P., D. Gallant, C. Mercier [1980] "Pisum sativum and Vicia faba carbohydrates: Studies of fractions obtained after dry and wet protein extraction processes," J. Food Sci. 45:1629-1636) isolated by a wet process starches from air classified pea and fababean fractions. The isolation was not possible from starchy by-products probably due to their high hemicellulose content. Ningsanond et al. (Ningsanond, S., B. Ooraikul [ 1989] "Chemical and nutritional properties of dry and wet milling products of red cowpeas," Can. Inst. Food Sci. Technol. J. 22:147-155) describe wet and dry processes for fractionation of dehulled and milled cowpea seeds into protein-rich and starch-rich fractions. The dry process involves pin milling and air classification; the wet process involves wet milling of soaked whole seeds, alkaline extraction (pH 9), and acid-heat precipitation (pH 4.4 at 80.degree.).
There has been particular interest in split and broken garbanzo beans since there is very little market for these products other than grinding them up and using them for animal feed. Splits or brokens are a by-product of marketing whole garbanzo beans. The price of the brokens is about 1/10 of that of the whole beans. Most of the brokens are incorporated into feeds.
Stone-milled garbanzo bean flour is commercially available. However, the flour is creamy in color with a wide variation of particle size. It does not hydrate well and thus is not good for incorporation into foods and instead is most often used for feed.
Currently, there is no efficient method for the isolation of highly pure starch from legumes.